Identifiers that do not comply with all the rules for identifiers must be delimited in a Transact-SQL statement. For example:

SELECT *
FROM [My Table] --Identifier contains a space and uses a reserved keyword.
WHERE [order] = 10 --Identifier is a reserved keyword.

Both regular and delimited identifiers must contain from 1 through 128 characters. For local temporary tables, the identifier can have a maximum of 116 characters.

Rules for Regular Identifiers

The names of variables, functions, and stored procedures must comply with the following rules for Transact-SQL identifiers.

The first character must be one of the following:

A letter as defined by the Unicode Standard 3.2. The Unicode definition of letters includes Latin characters from a through z, from A through Z, and also letter characters from other languages.

The underscore (_), at sign (@), or number sign (#).Certain symbols at the beginning of an identifier have special meaning in SQL Server. A regular identifier that starts with the at sign always denotes a local variable or parameter and cannot be used as the name of any other type of object. An identifier that starts with a number sign denotes a temporary table or procedure. An identifier that starts with double number signs (##) denotes a global temporary object. Although the number sign or double number sign characters can be used to begin the names of other types of objects, we do not recommend this practice.

Some Transact-SQL functions have names that start with double at signs (@@). To avoid confusion with these functions, you should not use names that start with @@.

Subsequent characters can include the following:

Letters as defined in the Unicode Standard 3.2.

Decimal numbers from either Basic Latin or other national scripts.

The at sign, dollar sign ($), number sign, or underscore.

The identifier must not be a Transact-SQL reserved word. SQL Server reserves both the uppercase and lowercase versions of reserved words. When identifiers are used in Transact-SQL statements, the identifiers that do not comply with these rules must be delimited by double quotation marks or brackets. The words that are reserved depend on the database compatibility level. This level can be set by using the ALTER DATABASE statement.

Embedded spaces or special characters are not allowed.

Supplementary characters are not allowed.When identifiers are used in Transact-SQL statements, the identifiers that do not comply with these rules must be delimited by double quotation marks or brackets.

Note

Some rules for the format of regular identifiers depend on the database compatibility level. This level can be set by using ALTER DATABASE.